Kathryn Lehman, a Holland & Knight lobbyist who has worked with Freedom to Marry to overturn DOMA, says: "For those GLBT couples who are lawfully married in their states, it means the federal government will no longer be able to discriminate against them, and they will be eligible for federal protections and responsibilities afforded to all other married couples.''

It's much less clear what it means for same-sex couples married in one state but living in another that doesn't recognize gay marriage. There are more than 1,000 federal laws in which marital status matters, covering everything from income and inheritance taxes to health benefits and pensions. As NPR reports, some federal agencies adhere to what is known as a "place of celebration" standard. That means no matter where a couple is legally married anywhere in the world, the union is recognized for the purpose of federal benefits.

But other agencies, including the Internal Revenue Service and the Social Security Administration, hew to a "place of residence" standard. Marriage has to be recognized in the place the couple is living for them to be eligible for those federal spousal benefits.

The Obama administration and Congress will have to sort out many of the details.

What happens in California?

The court cleared the way for same-sex marriages to resume in California as the justices, in a procedural ruling, turned away the defenders of Proposition 8, the ballot question that added the ban to California's Constitution. The court's action, while not a sweeping ruling, sends the case back to California, where state and federal judges and the state's top officials have said same-sex marriage is a matter of equal rights. Gov. Jerry Brown says county clerks must begin issuing marriage licenses to same-sex couples as soon as a federal appeals court lifts a ruling that was temporarily making same-sex unions illegal. That will take at least 25 days, although a federal appeals court there said it may continue to bar gay marriages even longer if proponents of Proposition 8 ask for a rehearing.

What happens in Florida?

Nothing right away. In 2008, nearly 62 percent of Florida voters approved putting a same-sex marriage ban in the Florida Constitution. Gov. Rick Scott, reacting to the rulings, said: "It impacted federal law, not state law. . . . As the governor of this state, I'll uphold the law of the land, and that's the law of our state." The gay rights group Equality Florida last week announced the "Get Engaged" campaign, the center of the organization's push to legalize same-sex marriage in Florida. Education will be part of the campaign, but other functions are unclear.